The stability of a rock slope beside the Root 45, which has been qualitatively judged as “a dangerous slope” by many experts of the Ministry of Construction of Japan, is quantitatively evaluated by the analysis method that has already been proposed by the authors based on the homogenization theory, and the validity of the proposed analysis method is examined. In the analysis only graphical image of crack pattern and the mechanical properties of intact rocks consisting of the rock mass are used. The results analyzed show rather good evaluation for the “dangerous state” of the rock slope, and the validity and applicability of the method is confirmed.